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A cull could help save koalas from chlamydia, if we allowed it

Whether it’s sharks, crocodiles or kangaroos, culling animals is always a contentious topic. But when the iconic koala is the species for which culling is being advocated, it sparks even more interest and debate.

Such was the case this week when researchers from Queensland and New South Wales published a study recommending that koalas be culled in the name of conservation.

Their proposal is for the selective culling of individual koalas suffering from chlamydia in an attempt to reverse the disease’s impact on vulnerable populations.

Koala chlamydia

Chlamydia is a sexually transmitted bacterial disease (a different strain to that which afflicts humans) that causes infertility and blindness in koalas, and is one of several factors thought to be behind the decline of koala populations in the eastern states. Koalas suffering the disease gradually become weak, stop eating, and die.

Although affected koalas sometimes may be found and taken into care, to date there have not been any systematic programs to combat the disease in wild populations. Given the negative effects of chlamydia on koala populations in some regions there is an urgent need to look at management options, including one that may seem quite radical – culling diseased individuals.

The current study considered a declining population on the “Koala Coast” of south-east Queensland. The researchers used computer simulations to model several disease management scenarios. The simulation that had the most positive effect on long-term population growth involved culling chlamydia-infected koalas that were already sterile and dying, and treating other infected koalas with antibiotics.

The study found that, to grow the Koala Coast population, around 10% (or 140 individuals) of koalas would need to be captured and culled or treated each year.

Killing for conservation

The idea of culling diseased individuals to manage disease and its impacts on wildlife populations is not new, and has met with both success (such as with Chronic Wasting Disease in deer in North America) and dismal failure (in the case Devil Facial Tumour Disease in Tasmanian Devils).

The effectiveness of these programs depends largely on the behaviour and ecology of the host species, and the distribution and nature of the disease. When enough is known about these aspects, computer modelling is useful for determining the potential effectiveness of a selective culling approach and for helping guide management actions.

But while modelling may inform us that culling is scientifically the best management approach, deciding whether and how to go ahead is complex, even more so when koalas are involved.

Koala management is closely scrutinised both nationally and internationally. The koala is the only native Australian species for which culling has been consistently dismissed as a management option (for overabundant populations in the southern states).

In 1997, culling was proposed as a component of an integrated strategy to manage high density populations of koalas on Kangaroo Island, South Australia. Despite having a sound scientific basis and the endorsement of many experts, it sparked much outrage and ultimately led to a decision at the Commonwealth level that culling will not be considered for management of koalas.

This decision has resulted in millions of dollars being spent on fertility control and translocation programs in Victoria and South Australia over the last two decades. These programs attempt to address situations where overpopulation of koalas is causing significant damage to local ecosystems.

Although some have brought positive outcomes after many years of intensive effort (for instance at Kangaroo Island and Mount Eccles in Victoria), these interventions are logistically challenging, extremely costly, and sometimes may have poor welfare outcomes for individual koalas.

Consequently, “do nothing” is the default management approach for many situations. But this can have drastic consequences for koalas, their habitats, and the other species that rely on those habitats.

Such was the case at Cape Otway in late 2013 when the Victorian government’s “do nothing” approach led to unsustainably high koala population densities, causing widespread defoliation of trees and the starvation of thousands of koalas. Around 700 koalas in irreversibly poor condition were killed when the government finally intervened on animal welfare grounds. Meanwhile, thousands of koalas likely suffered a slow death out-of-sight.

Although some trees recovered following the dramatic decline in koala numbers, high fertility has resulted in the population increasing again, and another imminent starvation event.

We do it for other animals, why not koalas?

Many wildlife researchers and managers would argue that a better approach for these situations would be to cull some koalas when it is clear that even more koalas will die if no action is taken.

This is not to suggest that culling be undertaken indiscriminately, nor in all situations. But it should be considered in circumstances where science indicates that it is the most effective approach to maintaining a healthy ecosystem and population of koalas.

It is the same approach that is used for numerous other native species in Australia and worldwide, so why shouldn’t it be considered for koalas, too?

Considering the outrage over killing Cape Otway’s starving koalas to reduce suffering, it seems that there may be little public support for culling koalas for any reason. It will be interesting to see how this new proposal to cull diseased koalas in Queensland and New South Wales will be received.

There likely will be opposition to culling and more support for a “treatment only” approach, despite its lower predicted effectiveness. However, one would hope that decision-makers place more weight on the scientific rigour of the research behind the proposal rather than the emotive argument that it is wrong to cull koalas.